ASTR 1040 Accel Astro: Stars & Galaxies Prof. Juri Toomre TA: Kyle Augustson Lecture 17 Tues 11 Mar 08 zeus.colorado.edu/astr1040-toomre toomre Cas A SNR VLA - radio Today in Bizarre-Land Turn to evolution of massive stars through giant and supergiant phases: fusion occurs in `successive layers of onion End life as supernova explosion,, leaving behind either neutron star or black hole Pulsars fast spinning neutron stars with fierce magnetic fields; gradually slow down Synchrotron radiation makes the light seen as pulses and thus Crab nebula + pulsar shines (and pulses) brightly in many wavelengths Read 18.2 Neutron Stars and 18.3 Black Holes Recall Second Mid-Term Mon 17 Mar; Review Thur 13 Mar 7-9pm; 7 Observatory # 4 Wed 12 Mar 8-10pm (signup) Binary Systems: The Algol Paradox Algol is a binary system consisting of a 3.7 solar mass main sequence star and a 0.8 solar mass red giant.. Why is this strange? A. A. A 3.7 star should have become a red giant before a 0.8 solar mass star B. Binary stars usually have the same mass C. 0.8 solar mass stars usually never become red giants B. C. A. Clicker Puzzle: Algol Binary System A. Binary stars can have different masses but usually ARE formed at the same time. More massive star should have had a shorter main sequence lifetime What happened? Binary Mass Exchange The 0.8 solar mass star once was more massive (3.0), with a 1.5 mass companion As it became a red giant,, it swelled and poured material onto its companion (lost 2.2) early MS 3.0 1.5-2.2 Overview reminder: Life track of low-mass star The red giant (0.8) is now less massive than its companion (3.7) Future: : when the other star becomes red giant,, it may pour gas back? now 0.8 3.7 1
Clicker -- Paths in H-R H R Diagram Star moves upwards and to the right on the H-R R diagram. What is probably happening in the core? A. B. Core has just started to burn a new element B. Inner core is contracting and heating up; shell burning is increasing C. All nuclear burning is slowing down D. The inner core temperature is cooling B. HR diagram shifts B. Core is contracting and heating; shell burning is increasing Moving upwards on HR diagram means more luminosity more nuclear fusion This is usually due to the inner core heating due to gravitational collapse potential thermal faster burning Upward and to the right in H-R: H Giant phases in life track of low-mass star 10 6 Luminosity (solar units) Now consider evolution of massive stars after MS 10-4 40,000 Temperature 2,000 Evolution of massive stars Clock runs faster, can burn heavier elements First 4 steps pretty familiar, but no helium flash 1. 2. 3. 4. Successive core & shell fusion burning of C, O, Ne, Si.. all with alpha capture (or He) stars make many shallow H-R H R loops 5. 6. 2
Many layers of onion in massive star Fusion by helium-capture (alpha-particles particles ) burns C, O, Ne, Mg, Si.. layers of onion Core structure from successive burning stages: lesser elements on outside, heavier on inside Helium nucleus (2 protons) is absorbed,, energy is released Elements are created going up periodic table in steps of 2 Creation of elements from He-capture: evidence A few of many other fusion reactions also feasible in high-mass stars Even numbers favored! Mixture of elements in our near universe follows the pattern of He-capture fusion reactions, up to iron Even heavier elements are made by nucleosynthesis during supernova explosion High-mass zigs and zags in H-R H R diagram Elements of higher mass fusion burn successively, releasing energy to support the star against gravity. Reactions may change too fast for outer layers to respond,, so last zig/zags are small BIG Evolutionary SWINGS Cross the pulsational instability strip: Cepheids 3
Massive red giant or supergiant: Fierce hot winds and pulsed ejecta Wildest of all! ETA CARINAE Supermassive star (100 M SUN late in life, giant outburst 150 yr ago SUN ) Violent bipolar ejecta + disk at equator Hubble ST Red Giant or SG with intense brightening Evolution of V838 Light Echo (HST) `Light Echo from pulse Star V838 Monocerotis HST-ACS Onion-shell fusion burning stops with IRON (Fe, 26 protons ) CARTOON Actual mass / nuclear particle Iron does NOT release energy when it fuses! FUSION FISSION Iron does NOT release energy when it fuses! FUSION FISSION 4
Several fates for massive star 1. Strong winds shrink star, may end as WHITE DWARF Core Collapse SUPERNOVA Exploding remnant of massive star disperses heavy elements through the galaxy 2. Or core burns to Fe, eventually sudden CORE COLLAPSE! SUPERNOVA Inside may be a neutron star a remnant core of pure neutrons! Crab Nebula (M1), first seen as SUPERNOVA on 4 July 1054 from China -- visible in daytime Core collapse (massive star) SUPERNOVA Rapid disassembly of elements in core neutrons + neutrinos Neutron degeneracy pressure stiffens collapsing core --- + push of neutrinos envelope `bounces! SHELL BLOWS OFF SNR: Crab Nebula M1 4 July 1054 Observing Supernovae About 1 per century per galaxy (none in Milky Way since 1604 Kepler) [1572 Brahe; 1054 Crab; 1004 brightest] Crab SNR composite Oct 06: Spitzer (IR), Chandra (X), Hubble (V) Bright explosion visible for weeks/months - some visible in daytime! Remnant visible for 10,000+ years as huge bubbles and veils longer in radio 5
Was Crab SN recorded in Chaco?.and nothing recorded in Europe! Petroglyph from Chaco Canyon: Correct position relative to new moon for Crab Supernova, but some doubt Check this on your SkyGazer software Only supernova explosion creates elements heavier than iron: magic of nucleosynthesis SN shells, and what is left at center? Neutron stars More massive, smaller in size! Star with a crystal crust! Idea of neutron stars first suggested in 1930s (Landau, Zwicki, Baade, Oppenheimer) but seemed like wild dreaming. Favorite Postcard: Size of Neutron Stars Structure determined by gravity vs. neutron degeneracy pressure Size ~ 10 km.. More massive, smaller!! Crushing gravity at its surface, so not a nice neighbor or place to visit.. as tourist try Big Apple instead. STATEN ISLAND MAN BRONX QUEENS BROOKLYN Neutron star over NYC! Observing the`first Pulsar: BIG discovery 1.3 sec period Jocelyn Bell : Cambridge (UK) graduate student in 1967 (+ Anthony Hewish) ) discovered pulsars by accident Little Green Men (LGM)? Just WHAT could cause signal? Pulsar = rotating neutron star Fierce magnetic fields + sizzling electrons + fast rotation finest lighthouse Thomas Gold 1968 6
Pulsars and Neutron Stars Why pulsars spin so fast: Vast shrinking conserves angular momentum Collapse to a neutron star increases both rotation and magnetic fields Pulsars are lighthouses in our Galaxy! Newly collapsed neutron stars can rotate hundreds to thousands of times per second! Mystery resolved when pulsar discovered in Crab Nebula (known to be supernova remnant) -- Messier 1 or M1! The Crab pulsar also pulses in visual light 7